The formula for circumference is 2πr, where r = radius.
If you know the circumference is 43.5, then:
43.5 = 2πr
solve, first divide both sides by 2
21.75 = πr
next, divide both sides by π (or the approximation 3.14)
r ≈ 6.93
diameter is twice the radius ( d = 2r)
d = 2r
d = 2 x 6.93
d ≈ 13.86
The diameter is about 13.6 inches